215.kth-largest-element-in-an-array.md

Kth Largest Element in an Array

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Example 1:

Input: [3,2,1,5,6,4] and k = 2
Output: 5

Example 2:

Input: [3,2,3,1,2,4,5,5,6] and k = 4
Output: 4

Note:

You may assume k is always valid, 1 ≤ k ≤ array's length.

JavaScript

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var findKthLargest = function (nums, k) {
    let start = 0;
    let end = k - 1;
    debugger;
    return quickSort(nums, 0, nums.length - 1, nums.length - k);
};

function swap(items, firstIndex, secondIndex) {
    const temp = items[firstIndex];
    items[firstIndex] = items[secondIndex];
    items[secondIndex] = temp;
}

var partition = function (nums, start, end) {
    let pivot = nums[Math.floor((start + end) / 2)];
    let i = start;
    let j = end;

    while (i <= j) {
        while (nums[i] < pivot) {
            ++i;
        }
        while (nums[j] > pivot) {
            --j;
        }

        if (i <= j) {
            swap(nums, i, j);
            ++i;
            --j;
        }
    }

    return i;
};

var quickSort = function (nums, start, end, findIndex) {
    if (nums.length > 1) {
        let index = partition(nums, start, end);
        if (findIndex >= start && findIndex <= index - 1) {
            if (start < index - 1) {
                quickSort(nums, start, index - 1, findIndex);
            }
        } else {
            if (index < end) {
                quickSort(nums, index, end, findIndex);
            }
        }
    }

    console.log(nums);

    return nums[findIndex]
};

findKthLargest([3, 2, 1, 5, 6, 4], 2);